The present invention relates to vehicle suspensions and more particularly to an independent suspension for a vehicle having a floor which is disposed between the vehicle's wheels.
Lowering the cargo floor of a vehicle maximizes the height of the cargo space for any particular overall vehicle height, lowers the center of mass of the cargo improving vehicle stability, and makes loading easier. However, when the floor is lowered between the wheels, a suspended axle connecting wheels on each side of the vehicle is generally difficult, if not impractical, to achieve. An independent suspension system, connecting the wheels on each side of the vehicle to the vehicle itself, is usually required if the floor of the cargo space is to be located between the wheels at a level near or below the centers of rotation of the wheels. To take the greatest advantage of lowering the floor, the suspension should be compact to minimize the intrusion of the suspension into the cargo space and the height over the wheels should be minimized to permit loads to conveniently overhang the wheels. To improve the responsiveness of the suspension when traveling rough surfaces and to reduce the dynamic forces generated by the moving suspension components it is desirable to minimize the unsprung mass of the suspension system. However, the suspension system must be sufficiently strong to support the weight of the loaded vehicle as it travels over rough surfaces and to resist the forces of braking, rolling resistance, collision with obstacles, and lateral movement of the vehicle.
Smith, U.S. Pat. No. 5,275,430, discloses several independent suspensions for a vehicle with a lowered cargo floor. The suspensions feature a wheel support plate which is rotationally attached at a first end to the vehicle's frame. The wheel is attached to the wheel support plate between the frame attachment and an air spring interposed between the second end of the wheel support plate and the vehicle's frame. The air spring opposes the weight of the vehicle and road forces while providing for vertical motion of the wheel for travel over rough surfaces. Mounting the air spring either behind or above the wheel is disclosed. Protrusion of the suspension into the cargo space is minimized by the "thinness" of the wheel support plate. However, the moments resulting from the cantilevered wheel mounting are reacted through the relatively thin "thickness" of the wheel support plate and at closely spaced frame attachments. As a result, the wheel support plate is large and heavy increasing the unsprung mass and a complex lower link connecting the wheel support plate to the frame is necessary for the lateral stability of the wheel support plate. In addition, locating the air spring and the air brake actuator behind the wheel increases the distance between wheels for vehicles with multiple wheels increasing the force necessary to steer the vehicle and to otherwise control its lateral movement. On the other hand, locating the air spring and brake actuator above the wheel increases the height of the fender area over the wheel interfering with loads which overhang the wheels.
What is desired, therefore, is a rugged, compact independent suspension for a vehicle having a floor disposed between the supporting wheels. A suspension system which does not require additional stabilizing linkages and has a low unsprung mass is desirable.